An air fan relies on spinning blades to pressurize air to generate airflow. A conventional air fan has exposed blades driven by a motor to get spinning and a mesh type frame to surround the blades to avoid hurting people. But the frame still has gaps and small children could poke fingers inadvertently through the gaps of the frame and be injured by the high speed spinning blades. The frame also cannot prevent small articles from piercing through, hence small children could also insert incidentally playing articles into the frame to damage the articles or the blades. Moreover, the frame cannot prevent dust from accumulating on the blades. Unless the fan is washed and cleaned frequently the spinning blades could throw a great amount of dust outside to cause allergic implications on respiratory organs and skin of people after a prolonged period of time, or even inflict ailments.
Hence improvements of air fan have been constantly made. Now bladeless air fans with hidden blades have been developed and introduced on the market. For instance, R.O.C. Pat. No. M398032 entitled “Bladeless air fan” includes a base and a holder fastened to the base to house a motor, and a set of blades hinged on the motor. The holder has a latch portion on the top connecting to an air discharging portion which is a circular frame and has a slit air outlet behind the inner rim. The motor drives the blades spinning. Airflow generated by the blades blows upwards and is discharged through an annular air outlet at the air discharging portion. The blades are hidden in the holder without the risk of injuring children during spinning, and dust accumulating on the blades also can be reduced, and spreading of the dust can also be further reduced through the air discharging portion. However, its air outlet is located at the inner rear side of the air discharging portion and formed in a tortuous manner, airflow resistance passing through the air outlet increases and results in decrease of airflow power. As a result, the airflow power generated by the bladeless air fan is significantly smaller than the general air fan. The bladeless air fan is more expensive but does not provide desirable performance, hence is not well accepted on the market.
R.O.C. Pat. No. M394383 entitled “Bladeless air fan” provides another type of bladeless air fan that includes a frame and an airflow guiding means. The frame has an airflow passage and at least one airflow orifice set. The airflow guiding means is connected to the frame and has a hollow airflow guiding frame and an airflow guiding set. The airflow guiding frame has an airflow guiding passage communicating with the airflow passage. The airflow guiding set is located at a selected position in the airflow guiding passage to direct airflow direction and airflow speed of the air in the airflow guiding passage. Its airflow passage further is divided into an air intake passage and an air discharge passage. It also has a number of air inlets and air outlets formed alternately and annularly on the inner rim of the frame. It also has the drawback of inadequate airflow amount like the previous reference. In the reference of M398032 the annular air outlet surrounding the entire air discharging portion still cannot provide a greater amount of airflow. In the reference of M394383, with the air inlets and outlets located on the inner rim of the frame, the problem of inadequate airflow power also is unavoidable.
U.S. Pub. No. 2009/0060710 discloses another type of air fan to provide improved airflow discharge. It is a bladeless air fan including a nozzle, a device for creating an airflow through the nozzle and a mouth to channel the airflow in the nozzle. The mouth is located behind the inner rim of the nozzle. The mouth has a Coanda surface on the circumference. Through the Coanda effect of fluid kinetics the airflow tends to adhere to the Coanda surface and change the flow direction so that the airflow shifts to exit via the mouth at the rear side of the inner rim. While it has the advantage of balanced airflow because of the Coanda effect, the shifted airflow also generates resistance to the airflow and results in lower airflow exit speed.
In short, the aforesaid conventional techniques have the airflow generator located below the frame and result in constraint of frame swiveling. The conventional air discharge design also does not produce sufficient airflow power. There is still room for improvement.